Remove unused Draftail ImageBlock styles

client/src/components/Draftail/blocks/ImageBlock.scss

@@ -1,36 +1,6 @@
 @use 'sass:color';
 @use '../../../../../client/scss/tools' as *;
 
-@mixin wagtail-label-overrides {
-  float: none;
-  width: initial;
-  padding: 0;
-}
-
-.ImageBlock__field {
-  @include wagtail-label-overrides;
-  display: block;
-  margin-bottom: $button-spacing * 2;
-  color: theme('colors.surface-page');
-  cursor: pointer;
-}
-
-@mixin wagtail-input-overrides {
-  border: 0;
-  font-size: inherit;
-}
-
-.ImageBlock__field__input {
-  @include wagtail-input-overrides;
-  font-size: 1rem;
-  background-color: theme('colors.surface-field');
-  color: theme('colors.text-context');
-
-  &[readonly] {
-    color: theme('colors.border-field-inactive');
-  }
-}
-
 .ImageBlock__alt {
   @include font-smoothing;
   font-size: 0.875rem;